On our 2008 (26,000 miles), I've started to notice a "buzzing" noise (best way to describe it) from under the hood when the air conditioner is first turned on. Never noticed it before, but that doesn't mean it wasn't there. If I drive the car with the ac on, then park the car for 30 minutes or so, it seems to not occur when restarting the car and the ac. A little vague, I know. Sound normal to you?
There should be quite a few similar posts on here about this subject. It's the a/c compressor working. As it is electric rather than powered by the engine as in a normal car, you are more likely to hear it. I have found mine makes much more noise when you first turn it on when the car is hot inside. As the car cools inside, the compressor doesn't have to work so hard and gets quieter. When it has caught up getting the interior to temp it barely makes a noise. It did worry me somewhat when I first heard it myself. Hope this helps.
